The present invention relates to injection molding machines and relates, in particular, to such machines having the capability of operating a plurality of molds arranged in series.
The prior art shows injection molding machines having this capability. For example, U.S. Pat. No. 3,707,342, issued to A. Lohman on Dec. 26, 1972 shows two molds spaced apart in tandem with a dual nozzle injection unit positioned therebetween to fill the two molds alternately. No provision is made for separate means to stuff the molds.
An additional prior art patent pertinent to the present invention is U.S. Pat. No. 3,898,030, issued Aug. 5, 1975 to T. G. Bishop, entitled Injection-Mold Clamping Unit Having Alternately Ejecting Die Assemblies.
In this disclosure, latches 80A and 80B are used to couple separable mold halves 56A and 58A whereby single clamping and ejection units are used for both molds.
A further prior art patent is U.S. Pat. No. Re 28,721 reissued to J. J. Farrell on Feb. 24, 1976, entitled Time Saver plastic Draw-Back Valve Assembly. This patent discloses a primary reciprocating-screw injection unit 12 and an auxiliary injection piston 50 with a valve 52 for diverting molten plastic flow from the primary unit to the secondary unit thereby isolating the primary unit and permitting the secondary unit to "stuff" mold 32.
In addition, the prior art shows stack and sandwich mold arrangements wherein the mold cavity plates are disposed back to back separated by an integral hot runner. Stack or sandwich mold arrangements are well known in the art: however, their drawbacks include a less than optimum operating cycle and lack of versatility in components. Moreover, there is a disadvantage in combining a hot runner with mold elements as a single piece part. Such an arrangement necessitates replacement of a complete multiple element mold and hot runner as a unit when one wishes to change molds. Whereas when the mold elements are separable from the hot runner system, it is merely necessary to remove mold elements while the hot runner remains a machine fixture.
U.S. Pat. No. 4,539,171 to Sorensen is also of interest In the '171 patent, thermoplastic material is transferred from an injection unit to a sandwich mold by means of a so-called snorkel 30 and a cooperating nozzle 16. The snorkel and nozzle make a connection to provide a conduit for thermoplastic material. The snorkel and nozzle move relative to another along a common axis which is parallel to and spaced from central axis 13 along which clamping platens 10 and 11 reciprocate.
Additional publications of interest are U.S. Pat. No. 4,752,207, issued June 21, 1988 to Kaaden including a related brochure entitled "STUBBE--Twin-Station Injection-Moulding Machines" and a brochure by Stork Plastics Machinery entitled "Stork L-Type Injection Moulding Machine".
The '207 Patent and related Stubbe brochure (published October 1986) show a goose neck connection between a plastic injection unit and a distributor carried by a movable platen.
The Stork brochure (published on or about 1985) shows an injection unit disposed perpendicular to the mold clamp unit axis.